Dyes known as oxidation dyes, which are produced by oxidative coupling of a developer component with a coupling component, are preferred due to their intense colors and very good fastness. Nitrogen bases such as p-phenylenediamine derivatives, diaminopyridines, 4-aminopyrazolone derivatives, and heterocyclic hydrazones are generally used as developer substances. Phenols, naphthols, resorcinol derivatives, and pyrazolones are useful as coupling components.
Good oxidation dyestuff components must meet the following requirements:
They must produce the desired color nuances in sufficient intensity during oxidative coupling with the respective developer or coupling component. Also, they must possess a capacity for being absorbed by human hair, which capacity ranges from sufficient to very good; and, in addition, they should be toxicologically and dermatologically safe. The production of the strongest possible color shades closely corresponding to the natural color nuances is also important. Further, the general stability of the dyestuff produced as well as their fastness to light and to washing and their thermostability, have very special significance for the prevention of color shifts from the original color nuance or even a change in color to different shades.
Thus, the search for suitable oxidation hair dyes includes the task of finding the proper components that meet the above-mentioned prerequisites in an optimal fashion.